Bipolar plate for a fuel cell

ABSTRACT

A bipolar plate, which forms a first polar plate of a first base element of a fuel cell and a second polar plate of a second base element adjacent to the first base element of the fuel cell, includes two parallel plates. Each plate of the parallel plates includes at least one distribution channel formed in a thickness thereof, for distributing fuel or oxidant. Each distribution channel is arranged so that, when the first and second base elements of the fuel cell are stacked together, a flow channel is formed between the two parallel plates, and the flow channel communicates with a cooling fluid supply opening.

TECHNICAL FIELD

The present invention relates to the field of fuel cells, and inparticular that of bipolar plates used to form the stack of a fuel cell.In fact, a fuel cell is composed of a stack of electrochemical cellscomprising an anode and a cathode separated by an ion-exchange membrane,the electrodes being themselves arranged between two bipolar plates.

At the present time, numerous studies are being conducted on fuel cells,in the context of efforts being made to limit environmental pollution,notably in transport systems. Electrolytic generators based on hydrogenfuel, using air or pure oxygen as the oxidant, are unquestionably someof the most widely studied types at present.

PRIOR ART

As mentioned above, a fuel cell includes a stack of basic cells, eachcomprising an anode, a cathode and an ion-exchange membrane acting asthe electrolyte. During the operation of a fuel cell, two simultaneouselectrochemical reactions take place, namely oxidation of the fuel atthe anode and reduction of the oxidant at the cathode. These tworeactions produce positive and negative ions, which combine at themembrane to produce electricity in the form of a potential difference.In the case of an oxygen-hydrogen fuel cell, it is the H+ and O− ionsthat combine.

These electrochemical reactions take place in each basic cell, each ofthese cells being separated from the adjacent cells by bipolar plates,which have a number of functions, notably:

a first function of supplying the cell with fuel and oxidant, and

a second function of heat exchange, enabling the stack to berefrigerated or cooled.

It should be noted that a bipolar plate is generally composed of twothin plates, fixed together by a method such as welding or adhesivebonding. Additionally, bipolar plates, because of their differentfunctions must be electrically conductive, while remaining insensitiveto the oxidant and to the fuel in terms of corrosion.

To fulfil the first function, a channel is provided over the whole faceof the bipolar plates in contact with the membrane. Each channel has aninlet through which the fuel or the oxidant penetrates, and an outletthrough which are discharged the neutral gases, the water generated bythe electrochemical reaction, and the residual moisture of the hydrogen,for its part.

To fulfil the second function, a cooling liquid is generally passedbetween the two thin plates forming the bipolar plate. However, it hasbeen found that, in conventional bipolar plates, this cooling does nottake place correctly, as the cooling fluid does not flow through thewhole of the bipolar plate.

Patent application EP 1 358 691 discloses bipolar plates including pinsfitted between the two plates forming the bipolar plate, to ensure thatthere is sufficient space between the two plates to allow the flow ofthe cooling liquid. However, this solution has a number of drawbacks,notably in terms of ease of manufacture. It has also been found that itdoes not provide maximal cooling, since the flow of the cooling liquidis not uniform over the whole of the plate.

BRIEF DESCRIPTION OF THE INVENTION

Accordingly, the present invention aims to propose bipolar plates havingarrangements for improving the cooling of fuel cells. In another aspect,the present invention aims to propose bipolar plates having arrangementsfor strengthening the supply of fuel and/or oxidant.

Accordingly, the invention relates to a bipolar plate forming the firstpolar plate of a first base element of a fuel cell and the second polarplate of a second base element adjacent to the first base element of thesame fuel cell, comprising two parallel plates, each plate having atleast one channel for distributing fuel or oxidant, arranged in thethickness of the polar plate, and the bipolar plate being characterizedin that the distribution channels are arranged so that, when the firstand second base elements of the fuel cell are stacked together, a flowchannel is formed between the two polar plates, and in that thisdistribution channel communicates with a cooling fluid supply opening.

In a specific embodiment, the distribution of the channels on one faceof the bipolar plate is identical to the distribution of the channels onthe second plate of the bipolar face, except in an area in which thechannels are offset.

In a specific embodiment, the area in which the channels are offset isthe area in which, during the assembly of the bipolar plate, thehorizontal channels would coincide if there were no offset.

In a specific embodiment, the offset has a value of half a pitchupwards.

In a specific embodiment, the offset of the channels is created on theanode face of the bipolar plate.

In a specific embodiment, the offset channel elements have fixingpoints.

Another aspect of the invention relates to a bipolar plate forming thefirst polar plate of a first base element of a fuel cell and the secondpolar plate of a second base element adjacent to the first base elementof the same fuel cell, comprising two parallel plates, each plate havingat least one channel for distributing fuel or oxidant, formed in thethickness of the polar plate, the bipolar plate further comprising amanifold for the supply of fuel and/or oxidant, this manifoldcommunicating with the interior of the bipolar plate through openings.The bipolar plate is characterized in that it comprises a cut-out formedin one of the parallel plates, so as to allow a gas located in themanifold to enter the distribution channel via the openings and thecut-out.

In a specific embodiment, the bipolar plate has a first sealing element,located on the outer face of the bipolar plate in which the cut-out isformed, between the manifold and the cut-out, parallel to the cut-out.

In a specific embodiment, the first sealing element is a joint made of apolymer material.

In a specific embodiment, the bipolar plate includes, between thecut-out and the supply channels, a second sealing element for providinga seal between the gas inlet openings and a cooling liquid presentbetween the two parallel plates.

In a specific embodiment, the second sealing element is provided by ameans included in the group comprising welding, brazing, and adhesivebonding.

In a specific embodiment, the cut-out and/or the first sealing elementand/or the second sealing element extend over the whole length of themanifold.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will be clearly apparentfrom the following description of a preferred, but non-limiting,embodiment, illustrated by the following figures, in which:

FIG. 1 shows a first face of a bipolar plate according to the invention,

FIG. 2 shows a partial view, taken along a section line C-C, of thebipolar plate shown in FIG. 1,

FIG. 3 shows a second face of a bipolar plate according to theinvention,

FIGS. 4 and 5 show two cross sections, taken along A-A and B-Brespectively, through the bipolar plate shown in FIG. 3.

DESCRIPTION OF THE BEST EMBODIMENT OF THE INVENTION

A bipolar plate comprises a central skeleton 1 composed of two parallelthin plates, fixed together by a method such as adhesive bonding orwelding. One face of this plate is intended to be placed against ananode, in a fuel cell, and the other face is intended to be placedagainst a cathode.

Various terms are used in the following text, and are to be interpretedaccording to their definition given below:

-   -   the term “face of the bipolar plate” means the outer face of one        of the thin plates,    -   the “sides of the bipolar plate” are the four sides of the        rectangle forming the bipolar plate,    -   the term “horizontal” denotes an element parallel to the shorter        sides of the bipolar plate, and the term “vertical” denotes an        element parallel to the longer sides of the bipolar plate,    -   the term “top of the bipolar plate” denotes the edge of the        plate through which the gases and the cooling liquid enter,    -   the term “bottom of the bipolar plate” denotes the edge of the        plate through which the neutral gases and the cooling liquid are        discharged,    -   the term “anode bipolar face” denotes the face of the bipolar        plate which is to be placed in contact with an anode during the        assembly of the fuel cell, and    -   the term “cathode bipolar face” denotes the face of the bipolar        plate which is to be placed in contact with a cathode during the        assembly of the fuel cell.

The thin plates are pierced with a plurality of holes on theirperiphery, so as to form manifolds for fuel 2, oxidant 4, and coolingliquid 3. The plates also include a set of channels 5, formed in theirthickness, so as to allow the flow of fuel or oxidant on their surface.The thin plates also have openings 6 enabling a manifold to communicatewith a gas flow channel.

The present invention provides a bipolar plate having different channellayouts on each of the two faces of the bipolar plate. This is becausethe aim of the present invention is to propose a bipolar plate in whichthe distribution of the cooling fluid is uniform. For this purpose, thepresent invention proposes, in an advantageous embodiment, a channellayout enabling the cooling liquid to spread between the thin platesforming the bipolar plate.

In an advantageous embodiment, a first face of the bipolar plate has achannel layout as shown in FIG. 1, formed by a rectangular spiralcovering two thirds of the plate, and terminating, on the third third ofthe plate, in a coil of parallel lines.

In an advantageous embodiment shown in FIG. 3, the second face of thebipolar plate has a channel layout with horizontal elements of therectangular spiral offset upwardly in the vertical direction in the partof these elements located at the top of the central third of the bipolarplate. This offset is, for example, about half of a pitch.

More specifically, the area ZD1 in which the elements are offset is thearea in which, if two thin plates having the same channel layout wereassembled together, the horizontal elements of the channels wouldcoincide.

Thus, in the present invention, the assembly of a bipolar plate formedby a thin plate having a channel layout as shown in FIG. 1 and a thinplate having a channel layout as shown in FIG. 3 enables spaces to beprovided at the position of the entry of the cooling liquid, such thatthe liquid can spread into the whole of the bipolar plate. These spacesare visible in FIG. 5, which shows a sectional view of the bipolarplate, the section being taken at the position of an offset. Thus it canbe seen that the cooling liquid, penetrating between the bipolar platesthrough an opening 7, meets no obstacle on its passage towards thebottom of the bipolar plate, permitting a uniform distribution of thecooling liquid.

As mentioned above, the channel layouts are different on each of the twofaces of the bipolar plate. Thus the offset of the channels as explainedin the preceding paragraph may be provided on either the anode bipolarface or the cathode bipolar face.

In a preferred embodiment, however, the offset is provided on the anodeface. This is because the channels provided in the thin plate formingthe anode face of the bipolar plate are intended to carry hydrogen.Since hydrogen is a more fluid gas than oxygen, the offset formed in thechannel has little or no adverse effect on the movement of the hydrogenflow in the fuel cell.

Additionally, in another preferred embodiment, a similar offset of thechannels is provided in the bottom part of the bipolar plate, in an areaZD2. This offset in the bottom part is, for example, provided on thesame face of the bipolar plate as the offset provided in the top part ofthe bipolar plate. This offset formed in the bottom part facilitates thedischarge of the cooling liquid that has passed through the fuel cell.

In another preferred embodiment, the channel elements having an offsetalso comprise fixing points 8. These fixing points can be used, as shownin FIG. 4, to stiffen the bipolar plate during the assembly of the twothin plates, and to ensure that the channel formed between the twobipolar plates, and shown in FIG. 5, is not flattened during assembly.

Thus the present invention makes it possible to improve the cooling ofthe fuel cell without affecting its efficiency, since the flows ofhydrogen and oxygen gas required for the correct operation of the cellare not altered.

In another aspect, the invention also relates to a bipolar platecomprising a device for supplying gas to the fuel cell. An exemplaryembodiment of this plate is shown in FIGS. 1 and 2.

In one embodiment, the bipolar plate comprises a cut-out 10 formed inone face of the bipolar plate. This cut-out 10 is located between amanifold 4 for the supply of gas to the fuel cell and the channelsformed on the faces of the bipolar plate. Thus the gas located in themanifold 4 penetrates between the two thin plates via the openings 12and emerges from the space between the two plates through the cut-out10, or supply aperture, so that it then flows into the supply channels13 formed in the thickness of the thin plate in which the cut-out ismade. This movement of the gas is illustrated by the arrow marked 14.

In an advantageous embodiment, the bipolar plate also includes a joint,made of polymer material for example, located in the area indicated bythe arrow 15. A joint of the same type is positioned at the samelocation on the face of the bipolar plate intended to come into contactwith the face shown in FIG. 1. Thus, at the time of stacking, these twojoints provide a seal such that the gas flowing in the channels of thefirst plate does not come into contact with the gas flowing in the nextbipolar plate in the stack, these two gases being different in nature,thereby enabling the fuel cell to operate correctly. To allow thepassage of the gas illustrated by the arrow 14 under the bearing surfaceof the joint 15, the bearing surface of the joint 15 is raised above theother bearing areas of the joint where no passage of gas is requiredunder the joint.

A joint 16 also makes it possible to provide a seal between the two thinplates forming the bipolar plate, so that the gas following the pathindicated by the arrow 14 does not come into contact with the coolingliquid flowing in the bipolar plate.

This joint is, for example, formed by brazing, welding, adhesive bondingor any other means of forming a sealed connection.

In a preferred embodiment, the cut-out 10 and the two joints 15 and 16extend along the whole length of the manifold 4, the term “length” beingunderstood as extending over the whole horizontal part of the manifoldin the sense of the present invention.

Advantageously, this device may be installed, mutatis mutandis, on bothfaces of the plate, provided that it is located at the position of thehydrogen supply manifold on the anode face, and at the position of theoxygen supply manifold on the cathode face.

Thus the device of the present invention, comprising, notably, a cut-outand one or more sealing joints, allows gas to be supplied to the fuelcell while providing a seal between the two gases, for example hydrogenand oxygen, flowing in the fuel cell. The device can also be used toform a seal between the cooling liquid and the gases.

The two aspects of the present invention, namely the offsetting of thechannels to allow correct cooling of the bipolar plate, and the use of acut-out for the gas supply, may be used in combination or independentlyof one another.

It should be noted that similar elements have been indicated in thefigures by different references in order to clarify the arguments. Thusthe channels indicated by the reference 13 in FIG. 2 form the set ofchannels indicated by the reference 5 in FIGS. 1 and 3. Additionally,the openings indicated by references 6, 7 and 12 are openings of thesame kind.

Clearly, the invention is not limited to the examples described andillustrated, and various modifications can be made to it withoutdeparture from the scope of the invention as defined by the appendedclaims.

The invention claimed is:
 1. A bipolar plate, which forms a first polarplate of a first base element of a fuel cell and a second polar plate ofa second base element adjacent to the first base element of the fuelcell, the bipolar plate comprising: first and second parallel plates,each of the first and second parallel plates including distributionchannels formed in a thickness thereof, each of the distributionchannels being for distributing a fuel or an oxidant, wherein thedistribution channels are arranged so that, when the first and secondbase elements of the fuel cell are stacked together, a flow channel isformed between the two first and second parallel plates, and the flowchannel communicates with a cooling-fluid supply opening, wherein thedistribution channels of the first parallel plate have a region with anarrangement in which adjacent channels are nested to remain adjacent toeach other from an entry end, through a plurality of turns, to an exitend; wherein the distribution channels of the second parallel plate havea region with an arrangement in which adjacent channels are nested toremain adjacent to each other from an entry end, through a plurality ofturns, to an exit end; wherein the first parallel plate has a first faceand the second parallel plate has a second face, wherein, when the firstface and the second face are mated to face each other, first and secondareas are formed in the flow channel such that: (a) in the first area,an arrangement of horizontal elements forming part of the distributionchannels of the first parallel plate is aligned to coincide with anarrangement of horizontal elements forming part of the distributionchannels of the second parallel plate, the horizontal elements of thefirst and second parallel plates being elongated in a horizontaldirection, and (b) in the second area, the arrangement of the horizontalelements forming part of the distribution channels of the first parallelplate has an offset from the arrangement of the horizontal elementsforming part of the distribution channels of the second parallel plate,the offset being in a vertical direction that is perpendicular to thehorizontal direction, the vertical direction corresponding to a flowdirection from the cooling-fluid supply opening to a cooling-fluid exitopening, and (c) in the second area, the arrangement of the horizontalelements forming part of the distribution channels of the secondparallel plate does not have an offset in the vertical direction fromthe arrangement of the horizontal elements forming part of thedistribution channels of the second parallel plate in the first area,whereby the horizontal elements forming part of the distributionchannels of the second parallel plate in the second area and thehorizontal elements forming part of the distribution channels of thesecond parallel plate in the first area extend to one another in thehorizontal direction without offset in the vertical direction, whereinthe distribution channels of the first parallel plate include severaladjacent distribution channels that (1) extend linearly in parallel in afirst direction from a cut-out in the first parallel plate, the cut-outbeing located between a manifold for supplying a gas and thedistribution channels, toward an end of the first parallel plate otherthan an end where the cut-out is located, (2) turn together to reversedirection so as to extend linearly in parallel in a second directionopposite to the first direction, and (3) turn together again to reversedirection so as to extend linearly in the first direction beforeterminating, and wherein the offset is formed on an anode face of thebipolar plate and not on a cathode face of the bipolar plate.
 2. Thebipolar plate according to claim 1, wherein the vertical direction is adirection from a first edge of the bipolar plate, the first edge beingnearest to the cooling-fluid supply opening, to a second edge of thebipolar plate, the second edge being opposite the first edge.
 3. Thebipolar plate according to claim 1, wherein the offset has a value of ½pitch, and wherein the second area is within a central third, in thehorizontal direction, of the bipolar plate and not within the outertwo-thirds, in the horizontal direction, of the bipolar plate.
 4. Thebipolar plate according to claim 2, wherein the offset has a value of atleast ½ pitch.
 5. The bipolar plate according to claim 1, whereinhorizontal elements include fixing points.
 6. The bipolar plateaccording to claim 2, wherein horizontal elements include fixing points.7. The bipolar plate according to claim 3, wherein horizontal elementsinclude fixing points.
 8. The bipolar plate according to claim 4,wherein horizontal elements include fixing points.
 9. The bipolar plateaccording to claim 1, wherein the distribution channels of each of thefirst and second parallel plates are nested in a square wavearrangement.
 10. The bipolar plate according to claim 2, wherein each ofthe first and second parallel plates is structured to have first,second, and third sections arranged side-by-side in the horizontaldirection, each of the sections of a given parallel plate having: acommon first end at one of the first edge and the second edge and acommon second end at the other of the first edge and the second edge, inwhich: in the first section, the distribution channels: begin at thefirst end of the first section, run towards the second end of the firstsection in the vertical direction, and change direction at the secondend of the first section such that they run in the horizontal directionand enter the second section, in the second section, the distributionchannels: enter from the first section in the horizontal direction,change direction to run in the vertical direction, run towards the firstend of the second section in the vertical direction, and changedirection at the first end of the second section such that they run inthe horizontal direction and enter the third section, and in the thirdsection, the distribution channels: enter from the second section in thehorizontal direction, change direction to run in the vertical direction,run towards the second end of the third section in the verticaldirection, and terminate at the second end of the third section.
 11. Thebipolar plate according to claim 10, wherein the distribution channelsin the second area are located in the second section of the firstparallel plate.
 12. The bipolar plate according to claim 11, wherein thefirst end of each of the first, second, and third sections of the firstparallel plate corresponds to the second end of each of the first,second, and third sections of the second parallel plate.
 13. The bipolarplate according to claim 2, wherein, when the first face and the secondface are mated to face each other, a third area is formed in the flowchannel such that, in the third area, an arrangement of the distributionchannels of the first parallel plate has an offset from an arrangementof the distribution channels of the second parallel plate, and whereinthe third area is structured such that, during assembly of the bipolarplate, horizontal portions of the distribution channels in the first andsecond parallel plates are offset in the vertical direction.
 14. Thebipolar plate according to claim 13, wherein the second area is adjacentto the cooling-fluid supply opening, and the third area is adjacent tothe cooling-fluid exit opening.
 15. The bipolar plate according to claim1, wherein the arrangement of distribution channels of the first andsecond parallel plates is the same except in the second area.
 16. Thebipolar plate according to claim 9, wherein horizontal elements includefixing points.
 17. The bipolar plate according to claim 10, whereinhorizontal elements include fixing points.